Emergency hospital wards were set up during the 1918 flu pandemic.Credit: NATIONAL MUSEUM OF HEALTH AND MEDICINE/SPL
Of all the pathogens that have plagued humanity, few are as notorious and persistent as influenza. Its Houdini-like ability to regularly slip the shackles of vaccine- or infection-induced immunity, aided by a steady and sustained mutation rate, has created a seasonal viral scourge that wreaks medical and economic havoc all over the world. Here, Nature outlines the history of flu and how it evades attempts to control it.
A short history of flu pandemics
Influenza is never far away. Its seasonality means it see-saws between Northern and Southern hemispheres on an annual basis, causing illness and death among not just humans but also poultry, cattle and birds and mammals in the wild.
Nature Spotlight: Influenza
Every few decades or so, a chance mutation leads to an extraordinary pandemic event that can sweep the planet, claiming millions of lives. The 1918–19 flu pandemic caused 50 million deaths; for the 1957–58 pandemic it was 1 million to 4 million; in 1968–69, the death toll was also 1 million to 4 million; and in 2009–10 it was 105,000–395,000.
Seasonal flu causes 290,000–650,000 deaths, globally each year. In 2015, flu caused losses of US$8 billion in wages and productivity in the United States alone.
The multiple disguises of influenza
Influenza is a single-stranded RNA virus of the family Orthomyxovirus. Although the virus is most commonly referred to as flu, it has many names, subtypes and disguises. Alterations to two key proteins on the surface of the influenza A virus — the spike protein haemagglutinin that allows the virus to attach to host cells, and neuraminidase, which enables the virus to escape from host cells — mean that subtypes are identified according to variations in these proteins.
Of the four types of influenza, only type A causes pandemics. Influenza A (Alphainfluenzavirus) has 198 potential serotypes, consisting of combinations of the 18 known haemagglutinin (H) subtypes and the 11 known neuraminidase (N) subtypes.
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